Fuel economy

[Milky Bar Kid 1001]

I wonder if anyone can relate to this issue or offer advice.

I've 2008 (58 T25) 2.0lt D4D with 157,000 mls on the clock. When I first bought it (with 75,000 mls) I was getting almost 500 miles to a tank but over the years and especially now it now gets around 460 miles (less if I've used the A/C but I know this will drop the range any way so I take that into account). I service it every year (I was originally doing around 11/12,000 miles a year but now do around 7/8,000 miles a year) and use quality oil and decent oil filters (Blueprint) and change air filters when required. I've noticed some blow by when the engine is running and the oil filler cap is removed and oil residue on the inlet side of the turbo, but I'm assuming this from breather pipe which goes on to the air intake from the air filter. It's never really had the "pick up" on acceleration (I've driven other Avensis with the same engine and same (ish) mileage and they've seemed a lot quicker) and when I do/ give it a boot it has chucked out black smoke (I realise this is the unburnt fuel being dumped out) but it does a seem a bit thick. I've just checked the turbo with an endoscopy and I think it looks ok (if it doesn't then could someone let me know please!) but can't reach deep enough inside to reach the impeller and check for excessive movement. It does whistle on boost.

Any help/ advice greatly appreciated!!

Rich 😎😎